The present invention relates to automatic gain control circuits suitable for providing data which may be displayed in maximizing deflection within a scale while maintaining waveform shape adaptable for use with the system for providing a display indicative of analog display of a time varying signal with a time varying envelope such as a seismic recording system.
In seismic recording systems, it is desirable to provide displays of a plurality of traces in time registration, each trace being indicative of the currents of a signal received from a sensor. Each sensor signal is time varying and may commonly have a monotonically decreasing envelope. In order to maximize visibility of the information to be determined from the sample, it is desirable to provide for an automatic gain control in which scale deflection within a chosen maximum trace size for each sample is maximized while preserving the time varying shape of the waveform. A plurality of traces are viewed simultaneously to give an operator an indication of geological anaomalies.
Either wiggle traces or variable area traces may be viewed. In the generation of wiggle traces, the analog trace is displayed directly. In variable area traces, the apparatus includes means employing an algorithm for shading in areas beneath positive excursions of the analog level and a zero level to enhance visibility of the waveform.
Many different automatic gain control prior art embodiments have been provided. However, their ability to portray the input signals optimally (in terms of the above-described criteria) is limited either in terms of ability to match gain control signals to behaviour of the signal or in terms of complexity of the circuit providing suboptimal response time to accommodate time variations of input signal.